is there a way to code it so if a takeoff alternate is required it would recognize the alternate is within limits of that aircraft. per 14 CFR 121.617 the only limitation is the takeoff alternate for a two engine aircraft Not more than one hour from the departure [airport] at normal cruising speed in still air with one engine inoperative.
If the aircraft has 3 or more engines its not more than two hours from the departure [airport] at normal cruising speed in still air with one engine inoperative. This does not not have any thing to do with destination airports for instance the E175 max takeoff alt required is 300NM but I could have a 500NM destination alternate and still be within legalities for this flight to be dispatched and operated.